An aircraft contains various systems carrying out specific functions: weather radar, processing of flight parameters, electric generation, etc. These systems are composed of one or several electronic packages interconnected by communication links known as "Buses" and which in the aeronautical field are described by standards lodged at ARINC (Aeronautical Standardization office). Thus, for example, the standard ARINC 708 describes the weather radar system and the standard 717 describes the flight parameters acquisition system. Other buses comply with more general usage standards (for example, RS 232, 422 and 485 are standards published by the Electronic Industries Association), certain systems internally comprising buses particular to a package manufacturer.
A digital bus is thus a device for transmitting information between two systems. The information to be transmitted is digitized and may be represented by a series of 0's and 1's.
The digital buses mainly differ from one another via the following two characteristics:
the physical level which concerns the nature of the signals used and the way of coding binary information: for example, a condition 1 is represented by a voltage of 5 volts and a condition 0 by a voltage of 0 volts;
the protocol level which concerns additional information added to the initial message: these enable the recipient system to receive the initial information with the level of the desired security, for example the adding of a parity bit calculated from the transmitted binary information.
An automatic testing system intended to maintain electronic packages embarked on an aircraft is able to determine if a given package is operational and if the digital buses still observe their original specifications.
The following functions are required to verify the proper functioning of a bus:
generation of information on the bus in accordance with the protocol;
generation of information containing an error (non-observance of the protocol or tolerances concerning the signals) so as to check the proper functioning of the security of the system under test;
recording of information derived from the system being tested, said information being recovered by the computer of the automatic test system and analysed by the test program;
recording of protocol errors derived from the tested system;
generation of synchronization signals so as to carry out measurements relating to an event on the bus.
In order to maintain a fleet, an airline company needs to have this automatic test system. A system of this type shall be able to recreate around the package to be tested an environment identical to the one existing on the aircraft.
In order to test the packages embarked on an aircraft and connected by digital buses complying with different standards, the automatic test systems of the prior art are constituted by integrating a large number of simulation instruments, each being dedicated to a bus standard.
However, these systems have a large number of drawbacks and in particular:
the multiplication of the number of simulation instruments is expressed by an increase of the cost of the test system (each instrument has its own production cost);
the reliability and availability rate of the system deteriorates if the number of instruments increases;
a test system confronted during its functional life with the appearance on the market of new packages having buses not covered by the initial instruments shall of necessity integrate an additional instrument;
the size of the test system is encumbered by the amount of instruments.
The invention concerns a digital bus simulator integrated in an automatic test system able to carry out with a single instrument the simulation of various types of the digital buses of an aircraft.